Lonesome George: RIP On 24th June 2012, an animal that had been described as the rarest animal on Earth passed away. The animal had been resident at the Charles Darwin Research Centre (CDRC) on the island of Santa Cruz in the Galápagos Islands, and was the last individual of one of the famous Galápagos giant tortoise subspecies, made famous by their association with Charles Darwin. The tortoise had been discovered in 1972 on the island of Pinta and nicknamed George. He was quickly recognized as the last of his subspecies (Chelonoidis nigra abingdoni) the Pinta Island subspecies and because he was Lonesome George (image from Shutterstock) the last of his kind he became known as Lonesome George. Scientists estimate he was about 100 years old when he died. Over his time at the CDRC he became a symbol of the Galápagos Islands and the conservation efforts taking place there. Galápagos tortoises The Galápagos giant tortoise (Chelonoidis nigra) is the largest species of tortoise, and the 10th largest reptile on the planet. They can weigh over 250 kg (some 400 kg) and have shells measuring up to 1.5 meters, and are believed to live for more than 150 years. The word Galápagos is Spanish for saddle, which is the shape of some the subspecies shells, on the islands of Española and Pinta. These animals have long limbs and necks for reaching high vegetation. Other subspecies (which represent the largest animals) have a more rounded dome-shaped shell and shorter limbs and necks, and are found on Santa Cruz and from the Alcedo Volcano on Isabela. Scientists believe that tortoises arrived in the Islands by clinging to a piece of driftwood from a river mouth along the Pacific Coast. The closest living relative of the Galápagos tortoise (although not a direct ancestor), the Argentine tortoise (Chelonoidis chilensis), lives on the South American mainland. The divergence between C. chilensis and C. nigra probably took place 6 12 million years ago, preceding the volcanic formation of the oldest modern Galápagos Islands ca. 5 million years ago. Genetic studies show that the tortoises arrived in the oldest islands of the archipelago, San Cristobal and Española, and then spread throughout the Galápagos Islands. The evolutionary relationships between the subspecies thus echo the volcanic history of the Islands. Those on individual islands or in isolated parts of the larger islands developed into their own sub-species through restricted gene flow,
adapting to local conditions in the way described by Darwin (see Questions, below). On larger islands such as Santa Cruz, with humid highlands (over 800 meters in elevation), abundant lush grasses allowed the larger high-domed variety to graze. The saddleback subspecies originate from small islands less than 500 meters in elevation with dry, desert-like habitats (e.g. Española and Pinzón) that are more limited in food and other resources. The shell shape and long neck and limbs allow the animals to reach up and feed on plants such as the prickly pear. Examples of Galápagos tortoises (Chelonoidis nigra) The voyage of the Beagle At the time Charles Darwin visited the Galápagos Islands in 1835 a 5 week visit during the 5 year voyage of the Beagle (see textbook page 178) there were 15 subspecies of the Islands giant tortoise and they would have been found in their 100,000s. The death of Lonesome George marked the loss of an estimated fifth subspecies (three unverified and two recorded), leaving 10 remaining subspecies. Charles Darwin wrote about the Galápagos tortoises in his books and journals, and they had clearly influenced him as he developed his theory of evolution by natural selection. When Darwin arrived at the Galápagos Islands, the vice-governor of the Islands told him that he could identify what island the tortoise was from simply by looking at the shaped of the shell and other characteristics. Darwin wrote, in his Journal of researches into the natural history and geology of the countries visited during the voyage of H.M.S. Beagle round the world, under the Command of Capt. Fitz Roy (1845): The inhabitants... state that they can distinguish the tortoise from different islands; and that they differ not only in size, but in other characters. Captain Porter has described those from Charles and from the nearest island to it, namely Hood Island, as having their shells in front thick and turned up like a Spanish saddle, whilst the tortoises from James Island are rounder, blacker, and have a better taste when cooked.
Charles Darwin only reported seeing Galápagos tortoises on San Cristobal (at the time of Darwin s visit known as Chatham Island) subspecies chathamensis - and Santiago (James) Islands subspecies darwini. Both of these subspecies have an intermediate type of shell shape and are not particularly different in shape from one another, and so it is unlikely that Darwin would have drawn any useful conclusions to support his theory from these direct observations. At the time the comments of Captain Porter did not strike Darwin as important this only came later. Although he had specimens of shells from two islands, he had mixed these up and not recorded which shell had come from which island. On leaving the Galápagos, the ship had 30 adult tortoises on deck, although these were not for scientific study but a source of fresh meat for the Pacific crossing. Their shells and bones were thrown overboard, leaving no remains with which to test any hypothesis. It was only on reading his notes and combining the evidence of the tortoises with those of other animals that Darwin started to use them in the formulation of his new theory (see textbook page 177 179). He wrote in one of his research notebooks (Notebook B, Transmutation of species ): Animals on separate islands ought to become different if kept long enough apart with slightly differing circumstances. Now Galápagos Tortoises, Mocking birds, Falkland Fox, Chiloé fox, English and Irish Hare. Tortoise facts Poachers threaten Madagascar's rare tortoises, which include the Ploughshare, Spider, Radiated and Flat-tailed species. Radiated tortoises are one of the world's most beautiful species, according to Sir David Attenborough. They are only found in southern scrublands in Madagascar. Burmese starred tortoises are also listed as critically endangered (IUCN Red List). They get their name from the striking yellow and dark brown star pattern on their shells. Kleinmann's tortoise, also known as the Egyptian tortoise, is the smallest of the Mediterranean species. Leopard tortoise (Stigmochelys pardalis) found in southern and eastern Africa
Conservation in the Galápagos For thousands of years the tortoises enjoyed life free from predators. They were ideally suited for life in the Galápagos, whose sometimes barren terrain enabled them to survive with little food and water during times of drought. The arrival of adventurers, whalers and fisherman led to tortoises being hunted as a source of meat and oil. At the same time, these new arrivals to the Islands brought pigs, goats, horses and cows, which ate the Islands vegetation and crushed tortoise eggs and the soft shells of young tortoises. Before the arrival of man, Pinta Island, located in the north of the archipelago, was home to thousands of tortoises. Initially, female tortoises were collected as they were smaller and easier to handle when they became scarce the males were also collected depleting the population still further. During the 1950s fishermen working the nearby waters used the Islands to restock their meat supply whilst at sea; since tortoises were no longer available they released feral goats, which quickly multiplied and took over the island devouring the little island vegetation that existed. By 1972 the tortoise population had dwindled until only one adult male remained Lonesome George. In 1959 the Charles Darwin Foundation (CDF) was created, and the Galápagos National Park established. The CDF was established to carry out research for the conservation of Galápagos ecosystems, and to educate visitors to the Islands about natural history, issues concerning the Islands, and allow them to see the tortoise breeding project at work. More than 100 scientists, students and volunteers work with research and conservation projects to protect the Galápagos Islands and the endangered species they contain. In 1964 the Charles Darwin Research Centre was established on the island of Santa Cruz, which is where Lonesome George spent the last 40 years of his life. In 2007 UNESCO put the Islands on its World Heritage danger list, citing threats posed by invasive species, unchecked tourism and overfishing. With 185,000 visitors in 2011, it is clear that the Galápagos will never be the pristine wilderness it once was, although with careful control of tourism, and other conservation measures such as the removal of invasive species, it is hoped that that other species on the Islands will not follow Lonesome George into extinction. Breeding programme The Ecuadorian park service kept George at the Darwin Research Centre, where he became part of the Galápagos National Park Breeding Programme. Scientists made every effort to encourage him to breed with female tortoises from Wolf Volcano on Isabela (Wolf tortoises were found to be the closest morphologically and genetically to the Pinta tortoises). In July 2008, tortoise eggs were discovered in the pen that George shared with his female companions, although it was discovered that the eggs had not been fertilized and so could not develop. Despite the lack of success in re-establishing a population of Pinta tortoises, the conservation efforts in the Islands have resulted in the overall population of Galápagos giant tortoises growing to around 20,000, from a low in the 1970s of a few thousand. The Hood Island subspecies has recovered from a low of 15 to more than 1200. Nevertheless, the species is still classed as vulnerable by the International Union for Conservation of Nature (IUCN).
A new beginning? Tortoises living around Wolf Volcano on the Galápagos island of Isabela are hybrids and have genes from several subspecies. The interbreeding had been caused by whalers and pirates, who dumped tortoises on Isabela. These hybrid tortoises preserve genes from several subspecies thought to be extinct, including Pinta Island tortoises. At the University of Chicago in Illinois, scientists have begun sequencing Lonesome George's genome this will help identify tortoises that carry Pinta genes. A team of scientists is currently sampling tortoises from the region and looking for animals that carry Pinta DNA. In theory, by selectively breeding tortoises with the Pinta genes a new population of the subspecies could be created, although due to the slow reproduction rate of the tortoises it is likely that such a breeding programme would take many decades. The very people who ate and introduced invasive species to the Islands may therefore inadvertently, by moving tortoises to new areas resulting in hybrid animals, have left a solution for the re-establishment of the subspecies, saving the animals from extinction. Read further Lonesome George: The Life and Loves of a Conservation Icon, by Henry Nicholls. Published by Macmillan Science (2006) National Geographic report the death of Lonesome George History of Charles Darwin Foundation (CDF) Questions 1. Define the term species. [1 mark] 2. List three causes of isolation that that can lead to different species being produced. [3 marks] 3. Give one example for each of the isolating mechanisms listed in question 2. [3 marks] 4. Outline the mechanism of natural selection as a possible driving force for speciation. [5 marks] 5. Outline the role of plate activity on speciation. [4 marks] 6. Other than the reasons illustrated by the case of the Galápagos giant tortoise, what factors can cause species to become endangered or extinct? [4 marks] Total: [20 marks]
Suggested answers 1. A group of organisms that can interbreed and produce fertile offspring. [1 mark] 2. Geographical isolation; behavioural differences; anatomical differences; inability to produce fertile offspring. [3 max] 3. Geographical isolation: island formation, loss of land bridges, mountains Behavioural differences: different reproductive displays, songs, daily activity Anatomical differences: reproductive organs, size Inability to produce fertile offspring: genetic differences. [3 max] 4. Species show variation; all species over-produce; despite overproduction, population levels remain the same; over-production leads to competition for resources; the fittest, or best adapted organisms, survive; the survivors reproduce and pass on their adaptive genes to the next generation; over time, the population s gene pool changes and new species emerge. [5 max] 5. Speciation occurs as a result of isolation of populations; geographical barriers isolate populations of the same species; geographical barriers are mainly formed by plate tectonic movements e.g. mountain building; colonization of new islands, often formed by volcanic activity, can lead to adaptations of a species to specific environments; over time reproductive isolation will occur when members of the old and new species can no longer produce fertile offspring; e.g. Galápagos finches that have undergone speciation to fill many of the niches on the volcanic islands and they now are very different from the mainland ancestral finch; convergence of land masses produces a mixing of genetic pools, promoting new ecological links and possibly hybridization. [4 max] 6. Small population size; reduction in population size; the number of mature individuals / reproductive potential; geographic range and degree of fragmentation; quality of habitat; area of occupancy. [4 max]